Tube heat exchanger with liquid heat carrier



United States Patent TUBE HEAT EXCHANGER WITH LIQUID HEAT CARRIER UNITED STATES PATENTS 7/1906 Towne 10/1941 Kitto 3/1953 l-Iiersch 1/1963 Brown et a1..

12/1967 Sayre FOREIGN PATENTS 1 H1959 France 12/1955 Great Britain... 8/1943 Switzerland Primary ExaminerAlbert W. Davis, Jr.

References Cited.

AttorneyMcGlew and Toren ABSTRACT: A tube heat exchanger with liquid heat carrier g 8 Claims, 4 Drawing Figs.

U.S. Cl. 165/109, includes a cylindrical casing having a pair of partitions, one

23/288,I65/134,l65/159 adjacent each end, defining an upper chamber, a lower Int. Cl F281 13/12, chamber, and an intermediate chamber. Inner tubes for con- F28f9/24,F28d 7/00 ducting fluid to be heated or cooled extend between and Field of Search 165/159, through the partitions to interconnect the upper and lower 160, 161, 109, 134; 122/32; 23/288.92 chambers.

14 I II II I/ II 144/ w I,

[III/ll Ill I,

PATENTED DEC] 5 I976 SHEET 2 BF 2 TUBE HEAT EXCHANGER WITH LIQUID I-IEAT CARRIER BACKGROUND OF THE INVENTION Tube heat exchangers with liquid heat carrier and having inner tubes carrying the fluid to be heated or cooled, which inner tubes are surrounded by a coaxial covering tube to define an annular channel for the liquid heat carrier, are known. These tube heat exchangers which, in most cases have a plurality of mutually parallel inner tubes enclosed by respective covering tubes, can serve as drop film evaporators, for the concentrating of lye solutions, for example, or for carrying out chemical reactions for preparing phthalic acid anhydride, for example. Thus, they are useable, by'way of example, whenever an accurate temperature control along the tube is required and the quantities of heat to be supplied or extracted are large.

It is known, in heat exchangers of this type, to utilize a liquid salt as the liquid heat carrier. This presupposes that the annular channel between the inner tube and the covering tube has a relatively narrow cross section, for example an annular width of about 23mm. It is necessary that the channel width be as constant as possible not only in a circumferential direction but also over the entire length of the exchanger. With the high operating temperatures and large temperature differences of such tube exchangers, it is hardly possible toavoid a distortion or twisting of the individual tubes, since the covering tube and the inner tube do not distort to the same degree. This will necessarily lead to uncontrollable changes in the cross section of the annular channels.

Furthermore, with fluid flowing through a bundle of tubes to be heated or cooled by a liquid on the exterior of the tubes, the problem arises of how to carry the liquid in the space surrounding the tubes. If the fluid contained within the tubes is subject to a process which requires an accurate temperature control along the tubes, means for carrying the cooling or heating liquid, in the space surrounding the tubes, must be provided. It is known to use transverse baffle plates for this purpose, and these divert the heat carrier liquid through the length of the vertically arranged tubes and several times at right angles to the tubes. However, an exact temperature control in all tubes and along the axes of the tubes is not possible by this procedure. The conditions become worse the larger the number of tubes andthe shorter the length of each tube.

Another procedure for distributing the heat carrier evenly over the space surrounding the tubes comprises providing, centrally of this space, a circulating propeller, and the liquid heat carrier is distributed as uniformly as possible over a perforated plate extending at right angles to the tube axis and with a large number of perforations. With this arrangement, the heat carrier is indeed evenly distributed over the entire cross section of the reactor containing the tubes. However, along the tubes themselves no definite speed of the heating or cooling liquid, and thus no uniform transmission of heat, can be achieved.

These problems arise more particularly, for example, with a reactor for the production of phthalic acid anhydride. In this process, a gas is disposed inside the tubes, and this gas strongly acts over a catalyst and gives off heat. In order that the action can be properly controlled, this heat must be extracted. In practice, reactors with 8,000 tubes are used, and in this case the requirement is that all tubes be cooled uniformly along their length. To that end, a liquid salt, acting as a heat carrier, is circulated through the reactor at a temperature of 450 C. The temperature inside the tubes can rise to 500 C. or more.

To attain uniform cooling of the tubes, the above mentioned transverse baffle plates have hitherto been used, the circulating quantity of cooling liquid necessarily being of such a magnitude that, between the entry and exit of the liquid salt, only a few degrees of temperature difference exists. In spite of this, no assurance can be given that all the tubes are cooled absolutely equally.

SUMMARY OF THE INVENTION This invention relates to tube heat exchangers with liquid heat carriers and, more particularly, to a novel and improved 5 construction of such heat exchangers.

In accordance with the invention, the above mentioned drawbacks with respect to differential distortion of the inner and covering tubes are avoided by forming the covering tube with indentations of equal radial height distributed along its length and around its circumference. These indentations project into the annular channel for the liquid heat carrier and serve, on one hand, as range spacers to assure a constant cross section of the channel and, at the same time, serve as turbulence producers in the annular channel.

Drawbacks of the known forms of tube heat exchangers of liquid heat carriers are avoided by the present invention in that the bundle of tubes is mounted upright in a cylindrical case between a cover plate and a bottom plate, the opposite ends of the tubes opening outside of these plates. The casing space containing the tube bundle between the cover plate and the bottom plate is subdivided by an intermediate plate or partition into two superjacent chambers, one of which is connected with the inlet for the liquid heat carrier and the other of which is connected with the outlet for the liquid heat carri er. The covering tubes, provided with the aforementioned indentations, extend through the intermediate plate and communicate, on one end, directly below the cover plate and, on the other end, directly above the bottom plate, with a respective one of the two superjacent chambers.

The only connection between the superjacent chambers, and thus between the inlet and outlet of the heating or cooling liquid, lends through the channels formed between the individual tubes and their jackets into which the indentations of the jacket or cover tubes extend to serve simultaneously as range spacers spacing the covering tubes from the inner tubes, and as turbulent producers. The liquid heat carrier thus flows from the relatively large volume inlet chamber into the covering tubes, through the annular channels, and to the outlet chamber. As a result, not only is there a uniform distribution of the liquid heat carrier along all of the covering tubes but also there are equal, turbulent flow conditions along all of the tubes.

An object of the invention is to provide an improved tube heat exchanger utilizing a liquid heat carrier.

Another object of the invention is to provide such a heat exchanger including at least one inner tube for conducting fluid to be heated or cooled, with a covering tube surrounding the inner tube to define an annular channel for the liquid heat carrier and with the covering tube being formed with indentations at substantially equal radial height distributed longitudinally and circumferentially thereof.

' A further object of the invention is to provide such a heat exchanger in which a bundle of tubes is mounted upright in a casing between a cover plate and a bottom plate and open into respective top and bottom chambers defined by the cover plate and the bottom plate.

Another object of the invention is to provide such a heat exchanger in which the interior of the casing between the cover plate and the bottom plate is subdivided by an intermediate plate into two superjacent chambers, one connected with the inlet for the liquid heat carrier and the other connected with the outlet for the liquid heat carrier.

A further object of the invention is to provide such a heat exchanger in which the covering tubes, formed with the mentioned indentations, surround the respective inner tubes in the intermediate space and extend through the intermediate plate.

Another object of the invention is to provide such a heat exchanger in which each covering tube opens, at opposite ends, adjacent the cover plate and the bottom plate, respectively, to thus interconnect the two superjacent chambers of the intermediate space.

A further object of the invention is to provide such a heat changer in which the indentations in the covering tubes s We not only asrange spacers to maintain a uniform cross tion of the annular channels but also serveas turbulence ucers in the annular channels.

Another object of the invention is to provide such a heat e changer inzwhich there is a uniform distribution of the liquid at carrier over the lengths of the tubes and equal, turbulent w conditions-along all of the tubes. For an understanding of the principles of the invention, r mice is made to the following description of a typical embodimentthereof as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE'DRAWINGS DESCRIPTION'OF THE PREFERRED EMBODIMENT sReferring first to FIGS. l and 2, the illustrated reactor has a cylindrical casing 1 with an outwardly concave or arched coyer 1a and anoutwardly arched or concave base or bottom If); each of which is providedwith a respective fluid inlet or outlet. Casing I is provided witha substantially horizon-.

talj co ver plate 3 and a substantially.horizontal, bottom plate 4,

parallel tocover plate 3. A bundle Qfupright tubes 2 extend between, plates 3 and 4 and open therethrough into top chamber 5 and bottom chamber 6. The'narrow inner tubesyZ extending between plates 3'and '4 are tightly anchored in these plates, and the plates 3 and 4 define an intermediate space.

12in accordance with the invention, the space intermediate plates 3 and 4 is subdividedby an intermediate plate 7 into twof superjacent chambers 8 and 9. A lower connection 10 s'e'rv s as an inlet for the liquid. heat carrier into lower chamber 8,}while an upper connection 11, which-is diametrically opposite lower connection 10, serves: as an outlet for the liquid heat carrier from upper chamber .9. q That portion of each tube 2 within chambers 8 and 9 is surroundedby a respective coaxial covering tube 12. Tubes 12 have open top and bottom ends and extend in fluid-tight relat'icin' through intermediate plate 7. Each tube 12 opens at its :{directly underneath cover plate 3 into outlet chamber 9,

a'ndfopens at its bottom directly above bottom plate 4 into inlet chamber 8.

fiA's best seen in FIG. 3, the inlet openingslZa of covering tubes 12 are widened in the nature of a funnel. The space between each tube and. its respective covering tube 12 is, as coi'n'pared with the diameterof the tubes and particularly with thIeZ-tube-free volume of chambers 8 and 9, very small.

To assure a substantially uniform spacing of each. covering 12 from its associated inner tube 2, each; tube 12 is providedwith indentationsl3, 13a. which are distributed over the entire length and entire circumferenceof the covering tube, these indentations lying substantially. against, the associated inner tube 2. lndentationsl3, 13a succeedingone another in a direction longitudinally of each tube 2 are staggered circumferentially. relative to one another. The preferably hemisphericaljindentations 13,.13aprevent laminar flow from developing in the. narrow annular channel between each tube 2 and its covering tube 12'. By. thus assuring a strongly turbulent flow, especially high heat transmission values can;be obtained.

liquid salt at a temperature of 450 C., enters through inlet connection 10 into chamber 8 and distributes itself, in consequence of the large volume of the chamber, at a very low speed over the entire cross section of the'chamber. From this reservoir, and having practically the same pressure and the same temperature over its entire cross section, the liquid heat carrier enters the inlet openings 1240f covering tubes 12. The pressure, temperature and speed. of the liquid heat carrier in the covering tubes 12 along the innertubesl, containing the reacting gas, are thus the same for allof the tubes 12. The strongly turbulent cooling liquid flowing-through the covering tubest-lZ exits'at the upper ends of covering tubes 12 into chamber 9', where thespeed of. the cooling liquid decreases ,again so asto be. practically negligible. The cooling liquid leaves the reactor through connection 11. Since the two connections i0 and 11 are diametrically opposite each other, the inflow and outflow pressure losses, at right angles to the axes of the tubes, balance each other substantially completely.

The principal advantage of the tube exchanger of the invention is the definite speed and strong turbulence of the liquid heat carrier along the axes of the tubes, and this guarantees a much better heat transfer relative to the reactortubes than could be obtained with known liquid conducting means. Consequently, smaller heat transmission surfaces can be provided or, with smaller temperature differences, a more uniform cooling or heating can be achieved.

It will beunderstood that the above described conduction of the heating or cooling liquid, and the design of the covering tube or tubes, can be employed generally wherever a liquid medium for cooling or heating in a tube heat exchanger or an evaporator is used.

Whilea specific embodiment of the invention has been shown and described in; detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. V 3

lclaim: I

1. A tube heat exchanger with liquidheat carrier compris- 'ing, in combination, an upright substantially cylindrical casing having its upper end closed by a cover plate and its lower end closed by a bottom plate; a bundleofinner tubes, for conducting liquid to be heated or cooled disposed in a chamber defined by said casing, said coverplate and said bottom plate, each inner tube extending between said cover plate and said bottom plate and openingzexteriorly of, these plates; :1 plate in- In'o'peration, the above described reactor may include a termediate said cover plate and said bottom plate and dividing said chamberinto superjacent upper and lower subchambers, one of said subchambers having a. lateral chamber outlet opening and the other of said subchambers, having a lateral chamber inlet opening; saidplate being formed with apertures each having arespectiveinner tube extending therethrough; and a bundle of cover tubes disposed in said chamber, with each cover tube surrounding arespective inner tube in coaxially radially spaced relation therewith to define an annular channel for receiving the liquid heat carrier; each cover tube extending through a respective aperturein said intermediate plate and being supported. solely by said intermediate plate; the upper end of each eoveringtube opening into said upper subchamber directly below said cover plateand substantially above the lateral openingin saidsupper subchamber, and the lower end of each covering tube. opening into said lower subchamber directly above-said bottom plate and substantially below the lateral opening in said lower subchamber.

2. A tube heat exchanger with liquid heat carrier, as claimed in claim 1, in which said chamberinlet communicates with the lower of said two superjacent subchambers and said subchambers-outlet communicates with'the upper of said superjacent chambers.

3. A tubeheat exchanger with liquid heat carrier, as claimed in claim 2., in which said chamber inlet and said chamber out-" let are diametrically opposite, each other.

4. A tube heatlexchanger with liquid heat carrier, as claimed in; clairn3, inzwhich-each covering tube has a downwardly diverging liquid heat carrier inlet which is substantially funnelshape.

5. A tube heat exchanger with liquid heat carrier, as claimed in claim 1, in which said heat exchanger includes outwardly convex upper and lower end walls each defining, with the adjacent one of said cover and bottom plates, a chamber having an opening for the supply of fluid t said inner tubes and the extraction of fluid from said inner tubes. 1

6. A tube heat exchanger with liquid heat carrier, as claimed in claim 1, in which each covering tube is formed with indentations of substantially equal radial height distributed [on- 

